In the prior art, the controlling device for an electric fan has long been a variable reactor having a plurality of taps in series with the main winding of the electric fan motor. The speed reduction of the electric fan is obtained by selecting one of said taps step by step thrugh a switch. With this type of controlling means, the disadvantage results in that when the reduction speed of the electric fan is made by lowering the voltage applied to the electric fan through the action of said reactor, the efficiency of the electric fan is greatly decreased and a lot of heat is thus dissipated. The circuit connected in series with said reactor also reduces the power factor. Moreover, extremely low speed rotation could not be obtained through the control of such a device.
Though stepless, variable speed has been recently proposed in which a TRIAC or SCR is used as a switch means, stepless, variable speed is achieved by controlling the trigger retarding angle of a trigger pulse generator. This is merely making the change from step by step to stepless speed reduction. It does not make any contribution to the user. Furthermore, a phase control circuit of this type of controlling device for the electric fan is directly connected to the line voltage of commercial power supply and thus there is a likelihood of burning out some components thereof.
Another prior art type of speed recution device for an electric fan is a single-stage timer; in other words, the electric fan rotates at a predetermined speed for a period of time and then changes to a breezy speed of rotation. This aims to prevent people from catching cold after having gone to sleep with the fan on, especially weak or unhealthy people or babies. In any event, this type of controlling device does not meet the requirements of people. Another type of speed reduction device utilizes a multi-step timer. According to this type of controlling device, a timer switch from a first speed to a second speed, is divided into three stages, and the operational time period of each stage is fixed by manufacturers in advance so that the user cannot make any time period adjustment. Therefore, it still could not satisfy the requirement to enable people to meet any circumstance at any occasion.
In addition, the adjusting mechanism of the controlling device mentioned above easily gets out of order, is very large and heavy, and is costly and requires considerable maintenance.
Therefore, the object of the present invention is to provide an improved controlling device for an electric fan, wherein the speed reduction is gradually changed such that there is almost no awareness of speed variation during operation, and also speed reduction can efficiently be achieved to as low as 100 RPM.
Another object of the present invention is to provide an improved controlling device for the electric fan wherein the rotational speed variation is achieved by a stepless-delay-speed reduction to a predetermined value, and then reverse rotation with a sufficient speed to effect desired ventilation.
A further object of the present invention is to provide an improved controlling device wherein the speed adjustment of the electric fan is accomplished by generating a regular or irregular waveform to control said electric fan thereby producing with said fan an imitation of a natural breeze to make people feel more comfortable.
A still further object of the present invention is to provide a compact, low-cost, reliable, durable, light-weight, and semi-permanent, trouble-free solid state device.